FR2675279A1 - Direct projection device for screen printed screens, using an ultraviolet source - Google Patents

Abstract

Projection appliance (5) intended for ultraviolet insolation of a screen printing screen (4), comprising successively, on the same optical axis (6) and in the direction of the latter, a point-like source consisting of a lamp (9) emitting ultraviolet radiation, a light condenser (10), a support (11) for a film (22) to be projected onto the said screen printing screen, and an enlarging photographic lens (12), the abovementioned condenser being such that each point of the film constitutes the vertex of a radiation field enveloping the light source and enveloping the entry pupil of the abovementioned objective lens. The abovementioned condenser comprises successively, in the direction of the optical axis, a first lens (15) consisting of a convergent meniscus and a second (16) and a third (17) lens consisting of two plane-convex lenses, the convex faces of which are face-to-face.

Description

 The present invention relates to the field of screen printing and more particularly to the field of exposure by ultraviolet radiation of screen screens intended in particular for the manufacture of posters or pieces of posters.

 The technique traditionally used for the manufacture of screen printing screens is as follows. From an original small film, which corresponds to a poster or a piece of posters, an intermediate film is made in the actual format of the poster by enlarging the original, and this for each color to be printed. . This intermediate film is then placed on a mesh screen coated with a photosensitive layer, a vacuum is created to properly lay the film on the screen and the surface of the screen is exposed by ultraviolet radiation through the intermediate film. After skinning with water, this screen serves as a form to print.

 The object of the present invention is in particular to simplify the technique described above and in particular to eliminate the intermediate step consisting in the manufacture of the aforementioned intermediate film.

 The present invention relates more particularly to a method, an installation and a projection apparatus intended for the exposure by ultraviolet radiation of a screen printing screen.

 According to the invention, the projection apparatus intended for the ultraviolet exposure of a serigraphic screen can advantageously comprise successively, on the same optical axis and in the direction of the latter, a point source constituted by a lamp emitting a radiation. ultraviolet, a light condenser, a support for a film to be projected on said screen screen, and a photographic enlargement objective.

 According to one aspect of the invention, the aforementioned condenser is such that each point of the film constitutes the top of a radiation field enveloping the light source and enveloping the entrance pupil of the aforementioned objective.

 According to a preferred embodiment of the invention, the aforementioned condenser successively comprises, in the direction of the optical axis, a first lens constituted by a converging meniscus and a second and a third lens constituted by two plano-convex lenses whose faces convex are opposite.

 According to the invention, at least the aforementioned objective and the condenser are preferably adjustable in the direction of the optical axis of the camera.

 In a particular embodiment, said film support comprises a film-carrying plate engaged and movable horizontally in a chassis movable vertically.

 According to the invention, means for prepositioning the aforementioned plate and / or the aforementioned chassis are preferably provided.

 According to the invention, the aforementioned film support can advantageously comprise a film-carrying plate provided with hollow parts located under the film and connected to a suction source.

 According to the invention, between the film support and the objective is preferably provided a chamber delimited at its periphery by a bellows, means being provided for circulating cooling air in this chamber.

 According to the invention, the light source is preferably a microwave ultraviolet radiation lamp enclosed in a chamber trapping the microwaves and preventing the reflection of ultraviolet rays towards the condenser.

 According to the invention, at least the rear interior face of said enclosure is preferably covered with an absorbent layer, in particular black.

 According to the invention, the device is preferably mounted on a frame and the screen is mounted on a frame, these frames being movable relative to each other in the direction of the optical axis.

 According to the invention, the aforementioned device is preferably mounted on a movable frame in the direction of the optical axis.

The present invention will be better understood from the study of an installation for manufacturing screen printing screens, described by way of non-limiting example and illustrated by the drawing in which
- Figure 1 shows a side view in elevation of an installation for manufacturing a screen printing screen;
- Figure: 2 shows a vertical longitudinal section of the projection device of the installation shown in Figure 1;
- Figure 3 shows a longitudinal section of the optical structure of the above device;
- Figure 4 shows a cross section of the above apparatus, in the vicinity of the film to be projected;
- Figure 5 shows a vertical section along VV of Figure 4;
- and Figure 6 shows a horizontal section along
VI-VI of figure 4.

 Referring to FIG. 1, it can be seen that the installation generally identified by the reference 1 comprises a vertical frame 2 fixed to the ground, which carries on one of its faces, vertically, a frame 3 rectangular on which is stretched a screen printing screen 4 made of mesh nylon coated on its outer face with a photosensitive layer, the frame 3 being mounted on the frame 2 in a removable manner using known and conventional means.

 The installation 1 also includes, opposite and at a distance from the screen 4, a projection device generally identified by the reference 5, the optical axis 6 of which extends perpendicular to this screen 4 , which is mounted on a movable frame 7 in the direction of the axis 6 along slides 8 fixed to the ground.

 According to the optical axis 6 and spaced apart, the projection apparatus 5 comprises a point source constituted by a lamp 9 of spherical shape, with microwaves, emitting an ultraviolet radiation, a light condenser generally identified by the reference 10, a film support to be projected generally identified by the reference 11 and a photographic enlargement objective 12.

 The lamp 9 is placed in the center of a reflector 13 provided in front of the lamp 9 with a mesh grid 13a, thus forming an enclosure which makes it possible to trap the microwaves. The inner face of the reflector 13, which faces the condenser 10, is covered with a black coating preventing the reflection of light towards the condenser 10, so that only the direct ultraviolet radiation emitted by the lamp 9 reaches the condenser 10. A fan 14 is provided for cooling this lamp 9.

 The condenser 10 comprises, in the direction of the optical axis 6, three lenses 15, 16 and 17 which are carried by a frame 18 mounted on a longitudinal slide 19 of the frame 7.

 The lens 15 is constituted by a converging meniscus whose concave face 15a is turned towards the lamp. This lens 15 is large in relation to the lamp 9 so as to capture a large part of the light flux emitted by the latter.

 The two lenses 16 and 17 are identical and are plano-convex lenses, arranged in an opposite manner, their convex face 16a and 17a being opposite.

 As seen more particularly in FIGS. 4 to 6, the film support 11 comprises a vertical rectangular plate 20 which has a through passage 21 in front of which extends a film to be projected 22. This film-carrying plate 20 is movable horizontally through a frame 23 which itself is movable vertically along a vertical projecting part 24 of the frame 7.

 In the example shown, the upper edge of the film-carrying plate 20 has three notches 25 and the upper part of the frame 23 carries a ball 26 subjected to a spring 27 intended to engage in the notches 25.

 The three notches 25 correspond to three transverse prepositions of the film-carrying plate 20 with respect to the chassis 23 and consequently with respect to the optical axis 6.

 The chassis 23 is movable between two extreme vertical positions thanks to a jack 28 mounted on the frame 7 and which acts from below, to which correspond two vertical preset positions of the film-carrying plate 20 and consequently of the film 22 relative to optical axis 6.

 The film 22 is in abutment against a surface 29 of the plate 20 which is formed below its corresponding front face and in which are provided, under the film 22 and at the periphery of the latter, recessed parts formed by grooves 30 which are connected, by an orifice 31 formed in the plate 20 and to which an external duct 32 is connected, to a source of air suction allowing the film 22 to be pressed against the surface 29. This surface 29 is moreover provided, at its upper part, with slightly projecting lugs 33 penetrating into corresponding perforations of the film 22 and allowing its identical positioning on the film holder plate 20 each time.

 The objective 12 is mounted on a vertical support 34, the lower part of which is movably mounted on slides 35 of the frame 7.

 Between this support 34 and the vertical part 23 of the frame 7 is provided a bellows 36 providing a chamber 37. Around the objective 12 and in this chamber 37 is provided a nozzle 38 bringing the cooling air into this chamber 37, at through the support 34 and thanks to an external pipe 39.

 The installation described above works as follows.

 Thanks to the support 11, which allows six different positions of the film 22 relative to the optical axis 6, which each correspond to a piece of poster to be produced later, one of its parts is positioned along the optical axis by moving suitably the film-carrying plate 20 and the frame 23. This setting will be changed for the other parts, without the need to remove the film 22 or cut the latter.

 The chassis 7 is suitably positioned as a function of the enlargement that it is desired to obtain from the film 22 on the screen 4.

 The condenser 10 is suitably adjusted along its slides 19 and the objective 12 along its slides 35 at pre-indexed positions which are such that, as shown in FIG. 3, the lenses 15, 16 and 17 of the condenser 10 being designed for this purpose. Each point of the film 21 constitutes the top of a radiation field enveloping the lamp 9 and enveloping the pupil 12a of the objective 12. This means that the section of this radiation field and that of the lamp, in the same plane, correspond substantially.

 This is how the lens 15 captures a large part of the ultraviolet flux emitted directly by the lamp 9 and that the lenses 15 and 16 rectify the flux exiting from the lens 15 so as to make it as a whole converge towards the input 12a of goal 12.

 When the above adjustments are made, the screen printing screen 4 is exposed for a determined period.

 It is then possible to strip the exposed screen 4 with water in order to obtain a shape which will be used later during the printing operation, as is known to do.

 The installation which has just been described therefore allows direct implementation of screen printing screens 4 from an original film 22 of dimensions conventionally used because the operations of enlarging and insulating the screen 4 are carried out in a single operation using the projection device 5.

 The installation described above may have, in a particular concrete embodiment, the following dimensions.

 The lamp 9 can have a diameter of twenty five millimeters.

 The distance between the lamp 9 and the plane of the film 22 can be 0.450 meters.

 The radii of the convex face 15a and of the convex face 15b of the lens 15 can be 0.278 meters and 0.154 meters respectively, their distance on the optical axis 6 being 0.070 meters.

 The radius of the convex faces 16a and 17a of the lenses 16 and 17 can be 0.290 meters, the distance on the optical axis 6 of their convex face relative to their transverse planes being 0.070 meters.

 The diameter of the lens 15 can be 0.276 meters and the diameter of the lenses 16 and 17 can be 0.350 meters.

 The distance on the optical axis 6 between the lens 15 and the lens 16 can be 0.005 meters and the distance on the optical axis 6 between the two lenses 16 and 17 can be 0.005 meters.

 The condenser 5 can be adjustable along the optical axis 6 between 0.060 meters and 0.065 meters from the plane of the film 22.

 The entry plane 12a of the lens 12 can be adjustable between 0.400 meters and 0.450 meters from the plane of the film 22.

 The frame 7 can be adjustable between a distance of 2.5 and 5 mm from the frame 2 carrying the screen printing screen 4.

 The above installation is suitable, for example, for the production of screen-printing screens which can go up to 2 meters by 2.5 meters, from film of current dimensions 0.300 meters by 0.400 meters.

Claims (10)

 1. Projection device (5) intended for the ultraviolet exposure of a serigraphic screen (4), characterized in that it successively comprises, on the same optical axis (6) and in the direction of the latter, a point source (9) consisting of a lamp emitting ultraviolet radiation, a light condenser (10), a support (11) for a film (22) to be projected on said screen screen, and a photographic enlargement lens (12 ), the aforementioned condenser being such that each point of the film constitutes the top of a radiation field enveloping the light source and enveloping the entrance pupil of the abovementioned objective.  2. Apparatus according to claim 1, characterized in that the aforesaid condenser successively comprises, in the direction of the optical axis, a first lens (15) consisting of a converging meniscus and a second (16) and a third (17 ) lens constituted by two plano-convex lenses whose convex faces are opposite.  3. Apparatus according to one of claims 1 and 2, characterized in that at least the aforementioned objective (12) and the condenser (10) are adjustable in the direction of the optical axis.  4. Apparatus according to any one of the preceding claims, characterized in that said film support comprises a plate (20) film holder engaged and movable horizontally in a frame (23) movable vertically.  5. Apparatus according to claim 4, characterized in that prepositioning means (25) of the aforementioned plate and / or the aforementioned chassis (28) are provided.  6. Apparatus according to any one of the preceding claims, characterized in that the aforementioned film support comprises a film-carrying plate provided with hollow parts (30) located under the film and connected to a suction source.  7. Apparatus according to any one of the preceding claims, characterized in that between the film support and the objective is provided a chamber (37) delimited at its periphery by a bellows (36), means (38) being provided for circulating cooling air in this chamber.  8. Apparatus according to any one of the preceding claims, characterized in that the light source (9) is an ultraviolet microwave lamp enclosed in a chamber trapping microwaves and avoiding the reflection of ultraviolet towards the condenser .  9. Apparatus according to claim 8, characterized in that at least the rear inner face of said enclosure is covered with an absorbent layer, in particular black.  10. Apparatus according to any one of the preceding claims, characterized in that it is mounted on a frame (7) and that the screen is mounted on a frame (2), these frames being movable relative to one another. to each other in the direction of the optical axis.